Purpose: To study the prevalence and antimicrobial resistance of E. coli and Enterococcus in soil and vegetables in three urban gardens around Metro Detroit area.
Methods: Soil and vegetable samples were collected from three urban gardens in Detroit from June to October 2015. A total of 15 soil samples and 48 vegetable samples (leafy greens and root vegetables) were collected. E. coli was isolated by enriching samples in Lauryl Tryptose Broth, followed by spreading on MacConkey Agar. Enterococcus isolation was carried out by a selective enrichment in enterococcosel broth followed by growing bacteria on enterococcosel agar. Bacteria were then identified by PCR and analyzed by disc diffusion for the antimicrobial susceptibility profile. All bacteria from unique soil and vegetable samples were examined for their susceptibility to ampicillin, chloramphenicol, ciprofloxacin, streptomycin, and tetracycline. In addition, ceftriaxone and trimethoprim/sulfamethoxazole were tested for E. coli and erythromycin and vancomycin were tested for Enterococcus as well.
Results: Out of 15 soil samples, 6 (40%) were positive for E. coli and 14 (93%) for Enterococcus. Twenty-three (48%) vegetable samples were contaminated by E.coli and 39 (81%) by Enterococcus. Garden variation was observed in the bacteria prevalence indicating possible impact of soil amendment on the microbial composition. Disc diffusion results on bacteria from unique samples revealed common streptomycin resistance (70%) in Enterococcus, intermediate resistance of Enterococcus to ciprofloxacin (70%) and erythromycin (65%), and intermediate resistance of E. coli to ampicillin (95%).
Significance: Microorganisms prevalent in urban agricultural production may serve as an important source of food contamination and antimicrobial resistance.